Trial data can’t tell us everything about how effective vaccines are: we need to wait to see the real world impact
The delivery of Covid-19 vaccines continues apace in Britain and around the world, and soon we will have a lot of data on their initial effectiveness. Vaccines are vital tools that will help to rescue us from the pandemic, and most people accept them as part of everyday life. But many people have differing opinions about how they should best be used, and there is concern that vaccines won’t be as effective against new variants. Indeed, one study (which has not yet been peer reviewed) suggests that the Oxford/AstraZeneca vaccine provides only minimal protection against illness caused by the South African strain of Covid-19, meaning people may need a third jab later in the year to protect them from other variants. In any case, we need to understand what vaccines are, how we measure how well they work, and what they can and cannot do.